It is difficult to position a punch unit in association with a die to carry out hole punching, particularly, for example, in the punching of holes in the walls of tubes, molded vessels, extruded profile members and items of complex geometry enclosed in dies having inaccessible or difficult to access areas. Although holes in such items often may be drilled, punching is now preferred since commercially available cylinders have made for easier assembly of punch units and allow punching at a generally lower cost. In such circumstances the die may be used in conjunction with a pressurized fluid in contact with the rearward surface of the material as described in, for example, U.S. Pat. No. 3,487,668 to Fuchs, Jr. and U.S. Pat. No. 4,989,482 to Mason. In these hydroforming systems, die punches must be housed within the forming die block. As the punch is advanced to engage the forward surface of the material, the rearward surface of the workpiece is supported by the pressurized fluid. An indentation is achieved or a slug is sheared under the mechanical force applied to the material by the front edge of the punch and the force applied to the rearward surface of the workpiece by the pressurized fluid.
U.S. Pat. No. 2,173,358 to Ernst discloses a press with work ejector having a piston reciprocal therein. Ernst teaches a rather complicated system of hydraulic tubing. The piston extension port is located at the rear face of the unit, and the corresponding hydraulic piston retraction conduit extends around to the front face of the unit, then to the side of the unit. The piston retraction port is located on the front of the die punch unit, and the corresponding piston extension conduit extends around to the side of the unit. The unit is affixed by means of bolts at the front face of the unit.
U.S. Pat. No. 3,027,877 to Lansky discloses a fluid pressure motor for use in a die. Lansky's unit provides a cushioning means which will bring the piston to a smooth stop at the end of its stroke and which assists the piston in its return stroke. Lansky teaches a piston extension port and a piston retraction port on the rear face of the unit, and a restricter valve extending perpendicular to the unit. The unit is affixed by means of bolts at the front and rear faces of the unit.
U.S. Pat. No. 3,185,042 to Hastings and U.S. Pat. No. 3,188,923 to Mandelko teach pneumatic cylinders having pistons reciprocal therein. Both teach piston extension ports located at the rear face of the cylinder, and piston retraction ports located at the front face of the cylinder. Hastings teaches bolts at both the front and rear face of the cylinder, while Mandelko does not teach any apparatus for securing the cylinder to another apparatus.
None of the prior art teaches a pressure actuated piston and cylinder unit structured to facilitate and assist the housing of the unit in a forming die block. Known designs, such as those described above, are structured such that they are difficult to construct, having a multitude of parts which are subject to failure, and are difficult to install, service, and replace. Known designs also do not fit well into the often confined area of the forming die block and related machinery.